The invention relates to a method for regulating a welding current source with a current transformer, which has a series resonant circuit on the primary side and a parallel resonant circuit on the secondary side, the series resonant circuit being supplied with a variable alternating voltage by a bridge circuit and the parallel resonant circuit providing energy to a welding process by way of a rectifier, and a control unit controlling the bridge circuit in dependence on at least one state variable of the welding current source.
The invention also relates to a welding current source for carrying out the method.
Arc welding methods, in which an arc burns between a welding electrode and a workpiece, are known in various configurations. In these methods, an arc is ignited between a welding electrode and a workpiece and heats the end of the welding electrode on the arc side to such an extent that the material is transferred to the workpiece in the form of drops. The transfer of the drops may lead to the formation of a short circuit between the welding electrode and the workpiece, with the result that the welding current flowing from the welding electrode to the workpiece increases very strongly. In order that no spatter forms during the transfer to the workpiece, the welding current is usually regulated. For example, welding current sources in the form of so-called series-parallel resonant converters are known for this purpose. These comprise a current converter, usually a transformer, which has a series resonant circuit on the primary side and a parallel resonant circuit on the secondary side. The series resonant circuit is supplied with a variable alternating voltage by a bridge circuit and the parallel resonant circuit provides the required energy to the welding process by way of a rectifier. A control unit controls the bridge circuit in dependence on at least one state variable of the welding current source.
To regulate the welding current source, WO 01/53030 A1 proposes the use of two measuring devices for recording electrical-current state variables of the welding current source, to be specific a first measuring device, with which the primary current of the current transformer can be recorded, and a second measuring device, with which the secondary current of the current transformer can be recorded. The inclusion of the secondary current is necessary in the case of the regulating method disclosed in the cited document for establishing or calculating the pulse width of the alternating voltage. The recording of the secondary current requires either a shunt or a transducer which operates on the basis of the Hall principle. The use of a shunt involves a not inconsiderable power loss and the use of a transducer based on the Hall principle is relatively expensive.
It is therefore an object of the present invention to provide a method for regulating a welding current source of the type mentioned at the beginning that makes it possible for the welding current to be regulated at lower cost and with as little power loss as possible. Furthermore, it is intended to provide a welding current source for carrying out the method of this kind.